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Structure and evolution of solar supergranulation using SDO/HMI data
摘要： Context. Studying the motions on the solar surface is fundamental for understanding how turbulent convection transports energy and how magnetic fields are distributed across the solar surface. Aims. From horizontal velocity measurements all over the visible disc of the Sun and using data from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI), we investigate the structure and evolution of solar supergranulation. Methods. Horizontal velocity fields were measured by following the proper motions of solar granules using a newly developed version of the coherent structure tracking code. With this tool, maps of horizontal divergence were computed. We then segmented and identified supergranular cells and followed their histories by using spatio-temporal labelling. With this data set we derived the fundamental properties of supergranulation, including their motion. Results. We find values of the fundamental parameters of supergranulation similar to previous studies: a mean lifetime of 1.5 days and a mean diameter of 25 Mm. The tracking of individual supergranular cells reveals the solar differential rotation and a poleward circulation trend of the meridional flow. The shape of the derived differential rotation and meridional flow does not depend on the cell size. If there is a background magnetic field, the diverging flows in supergranules are weaker. Conclusions. This study confirms that supergranules are suitable tracers that may be used to investigate the large-scale flows of the solar convection as long as they are detectable enough on the surface.
关键词： Sun: granulation,Sun: photosphere,Sun: general
更新于2025-09-23 15:23:52
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The Spectral Content of <i>SDO</i> /AIA 1600 and 1700 ? Filters from Flare and Plage Observations
摘要： The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the lower solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the Transition Region and Coronal Explorer and Atmospheric Imaging Assembly (AIA; 1600 and 1700 ?) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without knowledge of the spectral contribution to these UV filters, the use of these rich imaging data sets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300–1900 ? from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600 ? is dominated by the C IV 1550 ? doublet (26%), Si I continua (20%), with smaller contributions from many other chromospheric lines such as C I 1561 and 1656 ? multiplets, He II 1640 ?, and Si II 1526 and 1533 ?. For the AIA 1700 ? band, the C I 1656 ? multiplet is the main contributor (38%), followed by He II 1640 (17%), and accompanied by a multitude of other, weaker chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.
关键词： Sun: UV radiation,Sun: flares,Sun: atmosphere,Sun: chromosphere,Sun: photosphere
更新于2025-09-23 15:22:29
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Proper horizontal photospheric flows in a filament channel
摘要： Context. An extended ?lament in the central part of the active region NOAA 11106 crossed the central meridian on Sept. 17, 2010 in the southern hemisphere. It has been observed in Hα with the THEMIS telescope in the Canary Islands and in 304 ? with the EUV imager (AIA) onboard the Solar Dynamic Observatory (SDO). Counterstreaming along the Hα threads and bright moving blobs (jets) along the 304 ? ?lament channel were observed during 10 h before the ?lament erupted at 17:03 UT. Aims. The aim of the paper is to understand the coupling between magnetic ?eld and convection in ?lament channels and relate the horizontal photospheric motions to the activity of the ?lament. Methods. An analysis of the proper photospheric motions using SDO/HMI continuum images with the new version of the coherent structure tracking (CST) algorithm developed to track granules, as well as the large scale photospheric ?ows, was performed for three hours. Using corks, we derived the passive scalar points and produced a map of the cork distribution in the ?lament channel. Averaging the velocity vectors in the southern hemisphere in each latitude in steps of 3.5 arcsec, we de?ned a pro?le of the di?erential rotation. Results. Supergranules are clearly identi?ed in the ?lament channel. Diverging ?ows inside the supergranules are similar in and out of the ?lament channel. Converging ?ows corresponding to the accumulation of corks are identi?ed well around the Hα ?lament feet and at the edges of the EUV ?lament channel. At these convergence points, the horizontal photospheric velocity may reach 1 km s?1, but with a mean velocity of 0.35 km s?1. In some locations, horizontal ?ows crossing the channel are detected, indicating eventually large scale vorticity. Conclusions. The coupling between convection and magnetic ?eld in the photosphere is relatively strong. The ?lament experienced the convection motions through its anchorage points with the photosphere, which are magnetized areas (ends, feet, lateral extensions of the EUV ?lament channel). From a large scale point-of-view, the di?erential rotation induced a shear of 0.1 km s?1 in the ?lament. From a small scale point-of-view, any convective motions favored the interaction of the parasitic polarities responsible for the anchorages of the ?lament to the photosphere with the surrounding network and may explain the activity of the ?lament.
关键词： prominences – Sun: photosphere – Sun: UV radiation – Sun: magnetic ?elds,Sun: ?laments
更新于2025-09-23 15:22:29
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Incorporating Surface Convection into a 3D Babcock–Leighton Solar Dynamo Model
摘要： The convective ?ows observed on the photosphere (e.g., supergranulation, granulation) play a key role in the Babcock–Leighton (BL) process to generate large-scale polar ?elds from sunspot ?elds. In most surface ?ux transport (SFT) and BL dynamo models, the dispersal and migration of surface ?elds are modeled as an effective turbulent diffusion. Recent SFT models have incorporated explicit, realistic convective ?ows in order to improve the ?delity of convective transport but, to our knowledge, this has not yet been implemented in previous BL models. We present the ?rst kinematic 3D Flux-Transport/BL model to explicitly incorporate realistic convective ?ows based on solar observations. Though we describe a means to generalize these ?ows to 3D, we ?nd that the kinematic small-scale dynamo action they produce disrupts the operation of the cyclic dynamo. The cyclic solution is found by limiting the convective ?ow to act only on the vertical radial component of the magnetic ?eld. The results obtained are generally in good agreement with the observed surface ?ux evolution and with non-convective models that have a turbulent diffusivity of the order of 3×1012 cm2 s?1 (300 km2 s?1). However, we ?nd that the use of a turbulent diffusivity underestimates the dynamo ef?ciency, producing weaker mean ?elds and a shorter cycle than in the convective models. Also, the convective models exhibit bands of mixed polarity in the polar regions that have no counterpart in solar observations, and the poleward migration speed of poloidal ?ux is determined mainly by the meridional ?ow and the vertical diffusion.
关键词： Sun: photosphere,Sun: magnetic ?elds,Sun: interior
更新于2025-09-23 15:21:21
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First simultaneous SST/CRISP and IRIS observations of a small-scale quiet Sun vortex
摘要： Context. Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations. Aims. We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated up?ows through the photosphere and chromosphere of a quiet Sun internetwork region. Methods. We analyzed high spatial and temporal resolution ground- and spaced-based observations of a quiet Sun region. The observations consist of high-cadence time series of wideband and narrowband images of both Hα 6563 ? and Ca II 8542 ? lines obtained with the CRisp Imaging SpectroPolarimeter (CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well as ultraviolet imaging and spectral data simultaneously obtained by the Interface Region Imaging Spectrograph (IRIS). Results. A small-scale vortex is observed for the ?rst time simultaneously in Hα, Ca II 8542 ?, and Mg II k lines. During the evolution of the vortex, Hα narrowband images at ?0.77 ? and Ca II 8542 ? narrowband images at ?0.5 ?, and their corresponding Doppler signal maps, clearly show consecutive high-speed up?ow events in the vortex region. These high-speed up?ows with a size of 0.5–1 Mm appear in the shape of spiral arms and exhibit two distinctive apparent motions in the plane of sky for a few minutes: (1) a swirling motion with an average speed of 13 km s?1 and (2) an expanding motion at a rate of 4–6 km s?1. Furthermore, the spectral analysis of Mg II k and Mg II subordinate lines in the vortex region indicates an upward velocity of up to ～8 km s?1 along with a higher temperature compared to the nearby quiet Sun chromosphere. Conclusions. The consecutive small-scale vortex events can heat the upper chromosphere by driving continuous high-speed up?ows through the lower atmosphere.
关键词： Sun: atmosphere,Sun: chromosphere,Sun: photosphere
更新于2025-09-23 15:21:21
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An open-source, massively parallel code for non-LTE synthesis and inversion of spectral lines and Zeeman-induced Stokes profiles
摘要： With the advent of a new generation of solar telescopes and instrumentation, interpreting chromospheric observations (in particular, spectropolarimetry) requires new, suitable diagnostic tools. This paper describes a new code, NICOLE, that has been designed for Stokes non-LTE radiative transfer, for synthesis and inversion of spectral lines and Zeeman-induced polarization profiles, spanning a wide range of atmospheric heights from the photosphere to the chromosphere. The code features a number of unique features and capabilities and has been built from scratch with a powerful parallelization scheme that makes it suitable for application on massive datasets using large supercomputers. The source code is written entirely in Fortran 90/2003 and complies strictly with the ANSI standards to ensure maximum compatibility and portability. It is being publicly released, with the idea of facilitating future branching by other groups to augment its capabilities.
关键词： Sun: photosphere,polarization,Sun: abundances,radiative transfer,Sun: chromosphere,Sun: magnetic fields
更新于2025-09-19 17:15:36
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Horizontal flow fields observed in Hinode G-band images
摘要： Context. Solar pores are penumbra-lacking magnetic features, that mark two important transitions in the spectrum of magnetohydrodynamic processes: (1) the magnetic field becomes sufficiently strong to suppress the convective energy transport and (2) at some critical point some pores develop a penumbra and become sunspots. Aims. The purpose of this statistical study is to comprehensively describe solar pores in terms of their size, perimeter, shape, photometric properties, and horizontal proper motions. The seeing-free and uniform data of the Japanese Hinode mission provide an opportunity to compare flow fields in the vicinity of pores in different environments and at various stages of their evolution. Methods. The extensive database of high-resolution G-band images observed with the Hinode Solar Optical Telescope (SOT) is a unique resource to derive statistical properties of pores using advanced digital image processing techniques. The study is based on two data sets: (1) photometric and morphological properties inferred from single G-band images cover almost seven years from 2006 October 25 to 2013 August 31; and (2) horizontal flow fields derived from 356 one-hour sequences of G-band images using local correlation tracking (LCT) for a shorter period of time from 2006 November 3 to 2008 January 6 comprising 13 active regions. Results. A total of 7643/2863 (single/time-averaged) pores builds the foundation of the statistical analysis. Pores are preferentially observed at low latitudes in the southern hemisphere during the deep minimum of solar cycle No. 23. This imbalance reverses during the rise of cycle No. 24, when the pores migrate from high to low latitudes. Pores are rarely encountered in quiet-Sun G-band images, and only about 10% of pores exist in isolation. In general, pores do not exhibit a circular shape. Typical aspect ratios of the semi-major and -minor axes are 3:2 when ellipses are fitted to pores. Smaller pores (more than two-thirds are smaller than 5 Mm2) tend to be more circular, and their boundaries are less corrugated. Both the area and perimeter length of pores obey log-normal frequency distributions. The frequency distribution of the intensity can be reproduced by two Gaussians representing dark and bright components. Bright features resembling umbral dots and even light bridges cover about 20% of the pores’ area. Averaged radial profiles show a peak in the intensity at normalized radius RN = r/Rpore = 2.1, followed by maxima of the divergence at RN = 2.3 and the radial component of the horizontal velocity at RN = 4.6. The divergence is negative within pores strongly suggesting converging flows towards the center of pores, whereas exterior flows are directed towards neighboring supergranular boundaries. The photometric radius of pores, where the intensity reaches quiet-Sun levels at RN = 1.4, corresponds to the position where the divergence is zero at RN = 1.6. Conclusions. Morphological and photometric properties as well as horizontal flow fields have been obtained for a statistically meaningful sample of pores. This provides critical boundary conditions for MHD simulations of magnetic flux concentrations, which eventually evolve into sunspots or just simply erode and fade away. Numerical models of pores (and sunspots) have to fit within these confines, and more importantly ensembles of pores have to agree with the frequency distributions of observed parameters.
关键词： methods: statistical,sunspots,Sun: activity,methods: data analysis,Sun: photosphere,techniques: image processing
更新于2025-09-19 17:15:36
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Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements
摘要： Context. One of the difficulties in extracting reliable information about the thermodynamical and magnetic properties of solar plasmas from spectropolarimetric observations is the presence of light dispersed inside the instruments, known as stray light. Aims. We aim to analyze quiet Sun observations after the spatial deconvolution of the data. We examine the validity of the deconvolution process with noisy data as we analyze the physical properties of quiet Sun magnetic elements. Methods. We used a regularization method that decouples the Stokes inversion from the deconvolution process, so that large maps can be quickly inverted without much additional computational burden. We applied the method on Hinode quiet Sun spectropolarimetric data. We examined the spatial and polarimetric properties of the deconvolved profiles, comparing them with the original data. After that, we inverted the Stokes profiles using the Stokes Inversion based on Response functions (SIR) code, which allow us to obtain the optical depth dependence of the atmospheric physical parameters. Results. The deconvolution process increases the contrast of continuum images and makes the magnetic structures sharper. The deconvolved Stokes I profiles reveal the presence of the Zeeman splitting while the Stokes V profiles significantly change their amplitude. The area and amplitude asymmetries of these profiles increase in absolute value after the deconvolution process. We inverted the original Stokes profiles from a magnetic element and found that the magnetic field intensity reproduces the overall behavior of theoretical magnetic flux tubes, that is, the magnetic field lines are vertical in the center of the structure and start to fan when we move far away from the center of the magnetic element. The magnetic field vector inferred from the deconvolved Stokes profiles also mimic a magnetic flux tube but in this case we found stronger field strengths and the gradients along the line-of-sight are larger for the magnetic field intensity and for its inclination. Moreover, the discontinuity between the magnetic and non magnetic environment in the flux tube gets sharper. Conclusions. The deconvolution process used in this paper reveals information that the smearing induced by the point spread function (PSF) of the telescope hides. Additionally, the deconvolution is done with a low computational load, making it appealing for its use on the analysis of large data sets.
关键词： Sun: photosphere,techniques: polarimetric,methods: statistical,methods: data analysis,Sun: magnetic fields,techniques: spectroscopic
更新于2025-09-19 17:15:36
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Energy and helicity budgets of solar quiet regions
摘要： Aims. We investigate the free magnetic energy and relative magnetic helicity budgets of solar quiet regions. Methods. Using a novel nonlinear force-free method that requires single solar vector magnetograms we calculated the instantaneous free magnetic energy and relative magnetic helicity budgets in 55 quiet-Sun vector magnetograms. Results. As in a previous work on active regions, we constructed here for the ?rst time the (free) energy-(relative) helicity diagram of quiet-Sun regions. We ?nd that quiet-Sun regions have no dominant sense of helicity and show monotonic correlations a) between free magnetic energy/relative helicity and magnetic network area and, consequently, b) between free magnetic energy and helicity. Free magnetic energy budgets of quiet-Sun regions represent a rather continuous extension of respective active-region budgets towards lower values, but the corresponding helicity transition is discontinuous because of the incoherence of the helicity sense in contrast to active regions. We furthermore estimated the instantaneous free magnetic-energy and relative magnetic-helicity budgets of the entire quiet Sun, as well as the respective budgets over an entire solar cycle. Conclusions. Derived instantaneous free magnetic energy budgets and, to a lesser extent, relative magnetic helicity budgets over the entire quiet Sun are similar to the respective budgets of a sizeable active region, while total budgets within a solar cycle are found to be higher than previously reported. Free-energy budgets are similar to the energy needed to power ?ne-scale structures residing at the network, such as mottles and spicules.
关键词： Sun: photosphere,Sun: chromosphere,Sun: magnetic ?elds
更新于2025-09-10 09:29:36
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Chromospheric impact of an exploding solar granule
摘要： Context. Observations of multi-wavelength and therefore height-dependent information following events throughout the solar atmosphere and unambiguously assigning a relation between these rapidly evolving layers are rare and difficult to obtain. Yet, they are crucial for our understanding of the physical processes that couple the different regimes in the solar atmosphere. Aims. We characterize the exploding granule event with simultaneous observations of Hinode spectropolarimetric data in the solar photosphere and Hinode broadband Ca ii H images combined with Interface Region Imaging Spectrograph (IRIS) slit spectra. We follow the evolution of an exploding granule and its connectivity throughout the atmosphere and analyze the dynamics of a magnetic element that has been affected by the abnormal granule. Methods. In addition to magnetic flux maps we use a local correlation tracking method to infer the horizontal velocity flows in the photosphere and apply a wavelet analysis on several IRIS chromospheric emission features such as Mg ii k2v and Mg ii k3 to detect oscillatory phenomena indicating wave propagation. Results. During the vigorous expansion of the abnormal granule we detect radially outward horizontal flows, causing, together with the horizontal flows from the surrounding granules, the magnetic elements in the bordering intergranular lanes to be squeezed and elongated. In reaction to the squeezing, we detect a chromospheric intensity and velocity oscillation pulse which we identify as an upward traveling hot shock front propagating clearly through the IRIS spectral line diagnostics of Mg ii h&k. Conclusions. Exploding granules can trigger upward-propagating shock fronts that dissipate in the chromosphere.
关键词： Sun: photosphere,Sun: chromosphere,Sun: oscillations
更新于2025-09-10 09:29:36